Physicists at the National Institute of Standards and Technology (NIST) have built a quantum simulator that can engineer interactions among hundreds of quantum bits (qubits)—10 times more than previous devices. As described in the April 26 issue of Nature*, the simulator has passed a series of important benchmarking tests and scientists are poised to study problems in material science that are impossible to model on conventional computers.
Many important problems in physics—especially low-temperature physics—remain poorly understood because the underlying quantum mechanics is vastly complex. Conventional computers—even supercomputers—are inadequate for simulating quantum systems with as few as 30 particles. Better computational tools are needed to understand and rationally design materials, such as high-temperature superconductors, whose properties are believed to depend on the collective quantum behavior of hundreds of particles.
Simulators exploit a property of quantum mechanics called superposition, wherein a quantum particle is made to be in two distinct states at the same time, for example, aligned and anti-aligned with an external magnetic field. So the number of states simultaneously available to 3 qubits, for example, is 8 and this number grows exponentially with the number of qubits: 2N states for N qubits.
Crucially, the NIST simulator also can engineer a second quantum property called entanglement between the qubits, so that even physically well separated particles may be made tightly interconnected.
Over the past decade, the same NIST research group has conducted record-setting experiments in quantum computing,** atomic clocks and, now, quantum simulation. In contrast with quantum computers, which are universal devices that someday may solve a wide variety of computational problems, simulators are "special purpose" devices designed to provide insight about specific problems.
This work was supported in part by the Defense Advanced Research Projects Agency. Co-authors from Georgetown University, North Carolina State University and in South Africa and Australia contributed to the research.
As a nonregulatory agency of the U.S. Department of Commerce, NIST promotes U.S. innovation and industrial competitiveness by advancing measurement science, standards and technology in ways that enhance economic security and improve our quality of life.
* J.W. Britton, B.C. Sawyer, A. Keith, C.-C. J. Wang, J.K. Freericks, H. Uys, M. J. Biercuk and J.J. Bollinger. Engineered 2D Ising interactions on a trapped-ion quantum simulator with hundreds of spins. Nature. (In press) doi:10.1038/nature10981.
** See the NIST 2009 news announcement, "NIST Develops Powerful Method of Suppressing Errors in Many Types of Quantum Computers."